This disclosure relates to a method of making modified polyalkylene terephthalate polymers and compositions and articles comprising the same.
Polyethylene terephthalate (also referred to as “PET”) is a polyester of terephthalic acid and ethylene glycol and can be obtained by the polycondensation of dimethyl terephthalate with ethylene glycol, or from terephthalic acid with ethylene glycol. PET can be amorphous and transparent or a semi-crystalline, opaque, and white thermoplastic material. PET can be chemically resistant to mineral oils, solvents, and acids, but can be susceptible to chemical attack by alkali. Semi-crystalline PET has good strength, ductility, stiffness, and hardness. Amorphous PET has better ductility than semi-crystalline PET, but less stiffness and hardness. PET is used to make bottles for soft drinks and other household, consumer, and industrial products.
Unfortunately, despite recycling efforts, billions of pounds of PET are dumped into landfills annually all over the world. Other PET that is not reused is incinerated. The substantial amount of PET that is disposed into landfills creates significant waste. The incineration of PET wastes significant resources that could be used more effectively.
Thermoplastic molding compositions based on polybutylene terephthalate (also referred to as “PBT”) and a filler are used in various applications. Although conventional PBT-filler molding compositions are useful in many applications, conventional PBT-filler molding compositions generally cannot be made from recycle sources of PBT due to the lack of availability of PBT recycle streams. PET, unlike PBT, is made in much larger quantities and is partially recovered from consumer wastes. If PET, especially scrap PET, could be converted to PBT suitable for use in molding compositions, this would be valuable in meeting the current need to effectively use underutilized scrap PET in PBT thermoplastic molding compositions.
U.S. Pat. No. 5,451,611 teaches a process for converting waste poly(ethylene terephthalate) to either poly(ethylene-co-butylene terephthalate) or poly(butylene terephthalate) (PBT) by reaction with 1,4-butanediol. In discussing the prior art, U.S. Pat. No. 5,451,611 indicates that in most of the processes it cites, the undesirable byproduct diethylene glycol is formed, which contaminates the final product and has to be removed by purification before the recovered products can be reused again. A principal object of U.S. Pat. No. 5,451,611 was to provide a process for converting poly(ethylene terephthalate) waste directly into another high value polymer without breaking down the poly(ethylene terephthalate) to its constituent monomers or oligomers. The patent discloses numerous examples in which a variety of polymers have a diol incorporated at various amounts. Example 11 shows a PBT polymer being formed with a complete replacement of ethylene glycol with 1,4-butanediol.
U.S. Pat. No. 5,266,601 teaches a process for making PBT from PET by reacting PET with 1,4-butanediol. A principal object of U.S. Pat. No. 5,266,601 was to produce PBT containing less than 1.0 wt. % units of ethylene glycol from PET scrap. Another principal objective of U.S. Pat. No. 5,266,601 was to develop a process that facilitates the reduction of THF generated in the process. U.S. Pat. No. 5,266,601 discloses the production of PBT having ethylene glycol groups in an amount that is less than 1 wt. %. U.S. Pat. No. 5,266,601 discloses that “[a]ny diethylene glycol units in the starting PET are also eliminated as completely as possible” (Col. 3, 11 37-38). The patent discloses “adding only enough 1,4BD [1,4-butanediol] to the PET as is necessary to yield a mixture that can be processed well at the reaction temperature.” The patent discloses that, depending on the PET used “up to 1.0 mol 1,4-BD per mol PET” can be used. In the instances where compositions contain more than 1 wt. % ethylene glycol, U.S. Pat. No. 5,266,601 presents these compositions in comparative examples. Such compositions are described as having “yellowish” and “slightly yellowish” color, respectively. It is not clear what standard is used in U.S. Pat. No. 5,266,601 to determine the weight percent reported, as the weight percent can reasonably be defined based on either (i) a divalent ethylene radical remaining after removal of hydroxyl groups from ethylene glycol, or (ii) a divalent radical remaining after removal of terminal hydrogen atoms from ethylene glycol. Each moiety has a different molecular weight and, as such, each moiety can produce a different value.
Japanese laid-open application 2005-89572 teaches a method for producing polybutylene terephthalate by transesterifying bis(2-hydroxyethyl) terephthalate with 1,4-butanediol in the presence of a transesterification reaction catalyst under a pressure of 1-54 kPa at a final temperature from 200 to 230° C. and then subjecting the reaction product to polycondensation. In one embodiment, the bis(2-hydroxyethyl) terephthalate is obtained by depolymerizing polyethylene terephthalate with excessive ethylene glycol, and purifying the depolymerized product. The patent teaches that transesterifying bis(2-hydroxyethyl) terephthalate with 1,4-butanediol under reduced pressure imparts favorable results.
Despite extensive efforts, there remains a long felt need to improve the use of PET scrap that is ordinarily incinerated or buried in landfills. U.S. Pat. No. 5,451,611, for instance, does not teach effective processes to break down PET into its constituent monomers or oligomers—a feature that can be commercially desirable. U.S. Pat. No. 5,451,611 does not provide meaningful guidelines for making compositions functionally similar to a PBT containing ethylene glycol in amounts other than trace amounts and in which exhibit melting temperatures are higher than those shown in its examples. Similarly, U.S. Pat. No. 5,266,601 does not provide meaningful details about how to make effective PBT materials with ethylene glycol in amounts more than 1.0 wt. % or with other residues that can be found in some PET scrap. Also, U.S. Pat. No. 5,266,601 does not disclose processes that can use excess 1,4-butanediol, relative to the PET scrap used, or processes that do not require that the diethylene glycol be “eliminated as completely as possible.”
For at least the foregoing reasons, there remains a need to develop a process for making PBT random copolymers from PET that have useful performance properties. In addition, there remains a need to develop articles from molding compositions that utilize PBT derived from PET and that have useful performance properties.